【正文】 o stable oscillations of predator and prey populations (Figure ) Stable oscillations Population density Predator equilibrium density b) PredatorPrey Models ? Three general cases (cont.) – A highly efficient predator can exploit a prey nearly down to its limiting rareness (Figure ) Increasing oscillations c) PredatorPrey Models ? All based on how efficient predator is ? Shift in isoclines – Prey starvation (shift to left) – Food enrichment (shift to right) (Figure ) K1 increases to K1* with enrichment Prey Predator Predator isocline remains unchanged “The paradox of enrichment” Prey isocline changes K1 K1* d) PredatorPrey Models – Food enrichment (shift to right) (cont.) 187。Predator isocline changes – “paradox enrichment” : Increases in nutrients or food destabilizes the system PredatorPrey Models ? Functional response – How an individual predator responds to prey density can affect how predators interact with prey (Figure ) I II III Number of prey eaten per predator Prey density PredatorPrey Models ? Functional response (cont.) – Three types ? Type I: Individuals consume more prey as prey density increases ? Type II: Predators can bee satiated and stop feeding, or limited by handling time. PredatorPrey Models – Three types (cont.) ? Type III: Feeding rate is similar to logistic curve。 cessation of hunting and removal of peting sheep and cattle also had an impact – Serengeti plains of eastern Africa ? Large predators have little effect on large mammal prey Field Studies of PredatorPrey Interactions – Serengeti plains of eastern Africa (cont.) ? Most prey taken are either injured or senile ? Contribute little to future generations ? Prey are migratory – Moose population on Michigan39。s Isle Royale (cont.) ? Wolffree existence until 1949. ? Durwood Allen (1958) began to track wolf and moose populations ? Trends in populations (Figure ) 60 0 10 20 30 40 50 Wolves 1955 1960 1965 1970 1975 1980 1985 1990 1995 1997 Moose Wolves Year 200 400 600 800 1000 1200 1400 1600 1800 2020 2200 2400 2600 Moose 0 Field Studies of PredatorPrey Interactions ? Trends in populations (cont.) – Wolf population 187。Severe nosedive in 1981 187。Increased steadily in the 1960s and 1970s 187。A record population of 2500 was reached in 1995, when the wolf population was low 187。Confounded in 1996 when the moose population crashed starvation Field Studies of PredatorPrey Interactions – Canada lynx and snowshoe hare ? Populations show dramatic cyclic oscillations every 9 to 11 years (Figure ) 20 40 60 80 100 120 20 40 60 80 100 120 140 160 180 200 Abundance of lynx Abundance of hares Abundance of lynx (x 1000) Abundance of hares (x 1000) 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 Field Studies of PredatorPrey Interactions – Canada lynx and snowshoe hare (cont.) ? Cycle has existed as long as records have existed (over 200 years) ? An example of intrinsically stable predatorprey relationship Introduced Predators ? Method for determining the effects of predators ? Dingo predations on kangaroos in Australia – Dingo ? Introduced species ? Largest Australian carnivore Introduced Predators – Dingo (cont.) ? Predator of imported sheep ? Eliminated from certain areas – Spectacular increases in native species 187。Over 20 fold increase in emus Introduced Predators – Dingo (cont.) ? Effects on feral pigs – Shortage of young pigs – Considerable impact on recruitment of pigs (Figure ) 0 60 40 20 20 40 60 Age class (years) Males (%) Females (%) 0 60 40 20 20 40 60 Males (%) Females (%) 6+ 56 45 34 23 12 .05 6+ 56 45 34 23 12 .05 Age class (years) (a) Dingoes present (a) Dingoes present Introduced Predators ? European foxes and feral cats in Australia – Damage domestic livestock – Effects when removed (Figure ) 0 20 40 60 Predators shot No shooting 1981 1982 Mean no. of rabbits per km of transect Introduced Predators ? Lamprey and the Great Lakes – Construction of Wetland Canal allowed lamprey to enter the Great Lakes – Dramatic reduction in lake trout (Figure ) Lake Huron Mean production 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 Lake Michigan Lake Superior Mean production Mean production 1930 1935 1940 1945 1950 1955 1960 Lake trout production (millions per pound) Introduced Predators ? Lamprey and the Great Lakes (cont.) – Trout recovered after lamprey population was reduced Field Experiments with Natural Systems ? Lions in South Africa – Kruger National Park, 1903 – Lions Shot – Number of large prey increased – Shooting of lions ends, 1960 – Wildebeast increase so much that their numbers had to be culled from 1965 to 1972 Field Experiments with Natural Systems ? Gray partridge, European game bird – Figure Field Experiments with Natural Systems ? Gray partridge, European game bird (cont.) – Over 20 million shot in Great Britain in the 1930s – Only million shot in the mid1980s ? High chick mortality due to starvation Field Experiments with Natural Systems – Only million shot in the mid1980s (cont.) ? Reduced insects due to introduction of herbicides in the 1950s was suspected ? However, smaller populations in areas where there was no control of predators by gamekeepers Field Experiments with Natural Systems – Only million shot in the mid1980s (cont.) ? Predation control increased – The number of partrid